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Installing Shower Cubicles

Nowadays, many fiberglass and acrylic shower stalls are almost as bulky as full-size bath/shower units. Because they are so large, they are often manufactured as two- or three-piece units and are assembled on-site before installation. Usually, reassembled multipiece units—whether baths or showers—are well engineered and watertight without relying on caulk. However, beads of silicon caulk with an anti-mildew additive applied to the joints and seams of these will help to prevent mildew-causing water and soap scum from collecting.

Whether or not the shower stall is one piece or multipiece, its installation is very similar to the installation of combination plastic bath/shower units. Of course, there won't be a W&O fitting to contend with, and unless the stall will be set on a slab, the shower drain can be fitted after the stall is in place. In any case, it's a good idea to hold off on the drain rough-in since the actual drain location on a stall can vary significantly from a manufacturer's tech sheet. It's better to just cut out a 12-in. by 12-in. hole in the subfloor, roughly centered on the drain opening (assuming, once again, that the framing has been laid out so that a joist isn't right in the way).

The biggest headache will be maneuvering the stall past the plumbing as it slides into its opening. As with combination bath/showers, leaving the valve unattached to the framing and pulling it back into the stud bay as the unit is slipped into place is one option, while another is to frame up the enclosing sidewall after the unit is in place.

Installing Shower Receptor

Setting a shower receptor is considerably easier than setting a bath because there is no W&O fitting and because it is smaller and lighter. Again, it's a good idea to verify the drainopening location from the actual unit because small variations can make the hookup to the DWV system a little difficult, particularly if the receptor is being installed on a slab. No matter what material the receptor is made from, the heavier and more rigid it is, the less likely it is that it will flex under foot, which could eventually cause leakage around the drain fitting. Setting the receptor in mortar is still a good idea and will help reduce flexing, but it isn't a substitute for quality construction in the first place.

I think that shower receptors, like baths, should be installed on a finish floor. After cutting out a 6-in. square opening roughly centered below the pan drain opening, the receptor can be set in its framed shower enclosure. In some cases, particularly corner showers, there won't be an enclosure, and the receptor will be attached directly to the wall framing. Be sure to level the receptor if necessary with shims, and if you use mortar underneath, be sure it's is bedded down securely. Use screws instead of nails in predrilled and countersunk holes to attach the nailing flanges to the framing.

Shower receptors either have integral drain fittings cast out of the same material as the pan itself, or a separate plastic or brass fitting, which is either cast into the receptor or installed later on. The 2-in.-diameter waste pipe extends into the shower-drain fitting and is sealed with a rubber bushing.

For unusual spaces and custom installations, a site-built shower is the best option. Rather than trying to fit a square peg (a prefabricated shower) into a round or irregular-shaped hole, the site-built shower allows for the creative use of space and materials, like a functional sculpture. Functional, of course, is the key word: A site-built shower that leaks can be a nightmare for both the builder and his clients. So while the surface materials of a shower might elicit oohs and aahs, it's the underlying construction and waterproofing and the details that make the shower work.

The heart of any site-built shower is the pan, or waterproofing lining that keeps moisture where it belongs. For many years, site-built showers utilized metal or hot-mopped pans to ensure that water wouldn't leak through the enclosure floor and into the subfloor and framing. While occasionally you'll still meet an installer who swears by these pans, more often now the pan will be made of a plastic material, and for good reason: The new plastic membranes are more durable and leak proof, and they have a much longer projected life span, usually more than 50 years. The two basic types of membrane materials are CPE (chlorinated polyethylene) and PVC (polyvinyl chloride). While these materials are available in different thicknesses, most local codes require the 40-mil.-thick variety. Chloraloy is the most widely used CPE membrane that I know of, while Composeal and Permaguard are two of the most widely used PVC liners. Most plastic-pan manufacturers also offer solvents, cements, accessories like preformed corners, and good technical support with their product.

A two-piece clamping drain works in conjunction with the plastic shower pan to contain and direct water into the DWV system. The lower half of the drain attaches to a nipple extending from the shower's P-trap, while the upper half bolts onto the lower half, clamping the membrane in between. Weep holes allow water that has seeped through the grout and into the mortar bed to run into the drain.

The floor of the shower needs a 1/4-in.-per-ft. slope to the drain, both for the surface water and for water that works its way down to the pan liner. So the pan should be installed on a sloped subfloor before the rest of the mortar bed is poured. This can be done either with a shimmed plywood subfloor, or by first floating a cement subfloor, using a 4:1 sand/cement mix and a latex additive. In addition, 2x12 blocking should be installed between the studs around the perimeter of the shower. If the shower walls will have a cement backer board, then the bottom of the studs should be notched slightly so that the surface of the membrane won't sit proud of the framing and bow the backer board inward when it is attached.

After the framing, subfloor, and bottom half of the subdrain assembly are in place, the pan material can be laid out. Many showers are larger than the 60-in. width that many of these pan materials are available in, so you may have to carefully weld together two pieces of material together before laying the piece in place on the shower subfloor. Follow the manufacturers' instructions carefully for solvent-welding these two pieces together, and leave plenty of time for the weld to dry (preferably overnight). When cutting the material to size, leave enough so that the membrane will extend about 10 in. up the wall (or at least 3 in. above the height of the finish curb), and be sure that there is enough material to totally wrap the curb. Before actually laying the material down, smooth away any sharp or rough edges and carefully sweep the subfloor clean.

Corners are the tricky part. Inside corners should be folded tightly into a "pig's ear" fold, using plenty of solvent to ensure that the corner lies flat. Outside corners, such as those found on curbs, will need some cutting and patching with solvent. Some manufacturers offer preformed corner patches to help make this joint more easily. Staples are the easiest way to secure the membrane to the framing, but be sure not to put any staples below the height of the finish curb.

The final step in preparing the pan is to cut out the drain opening and make a small incision to push the bolt heads through the membrane. A double bead of butyl caulk—one on the inside and one on the outside of the bolts—between the bottom half of the clamp and the underside of the membrane should keep the drain / membrane assembly from leaking after it's clamped together. Be sure to test the pan by plugging the drain, filling it with water to an inch or so above the drain, and leaving it overnight. If there is a leak, it's better to know about it now rather than later.

After the pan has passed the leak test, the mortar bed can be floated, again making sure that it maintains the 1/4-in.-per-ft. slope. Wire mesh—typically 20-gauge galvanized 1-in. mesh—will reinforce the mortar and help prevent cracking, as will a latex additive. A waterproofing additive like Anti-Hydro will significantly reduce the water-absorbing capability of the mortar bed. Before floating the mortar, place pea stone, tile chips, or some other similar-size object in front of the weep holes to ensure that water has a free passageway into the drain. Alternatively, a porous filter specially designed to be placed over the weep-hole openings is also available